Over the years, silicate glass such as borophosphosilicate glass (BPSG) has played a critical role as a pre-metal dielectric (PMD) insulator for semiconductor devices. Recently, the geometry of semiconductor devices has become increasingly smaller. For example, device geometry has diminished to sub 0.25 xcexcm levels and even to 0.15 xcexcm and beyond. Consequently, it has become much more difficult to properly fill the gaps of the interlayer dielectric layers, i.e. satisfy xe2x80x9cgap fillxe2x80x9d requirements.
Typically, the integrity of the shallow junctions of a semiconductor device can only be maintained by restricting the thermal budget requirements of post-junction flow processes. Such reduced thermal budgets are essential for keeping the lateral and vertical diffusion of dopants to a minimum and to maintain the ultra-shallow junction integrity of sub-micron devices. However, reducing thermal budgets in this manner poses a challenge to maintaining the gap-fill requirements and surface planarity desired for PMD BPSG films.
As mentioned above, traditional BPSG films and annealing techniques are no longer suitable for satisfying flow and xe2x80x9cgap fillxe2x80x9d requirements of interlayer dielectric layers. Complete gap fill is realistically only possible with these structures if the anneal process allows the flow of the deposited films.
In furnaces, the use of wet steam reflow processes has shown some improvement of BPSG flow over dry nitrogen under identical annealing conditions. As such, a wet steam reflow process is currently preferred over dry nitrogen in furnace flow processes. Similar to furnace applications, comparable studies have also been conducted for the use of wet steam in rapid thermal processing. These studies demonstrated similar reflow results for RTP processed BPSG films at significantly reduced process thermal budgets.
For example, RTP processed BPSG films for PMD have recently been demonstrated for 300-mm generation applications (see Schaffer. et al., Solid State Technology, p. 117, September 1997). During the demonstrations, the films were first densified in RTP, and then further planarized by chemical mechanical planarization (CMP). The films used in the 300-mm demonstrations were TEB/TEPo 7.05 B wt %/3.79 P wt % BPTEOS films. These films were deposited at 500xc2x0 C. with their dopant levels verified by wet chemical analysis methods. The alternate dopant chemistries allowed higher dopant levels, thus accounting for the reduction of the flow temperature of these films.
Despite the above advances, a need nevertheless exists for BPSG films having improved chemistry. Moreover, a need exists for annealing techniques applicable to sub-micron devices that can optimize BPSG film properties to achieve superior stability, while also allowing BPSG film flow at reduced temperatures.
The present invention recognizes and addresses the foregoing disadvantages and others of prior art constructions and methods.
Accordingly, it is an object of the present invention to provide an improved method for forming layers in integrated circuits.
In general, the method includes the steps of processing an object, such as a semiconductor wafer, in a rapid thermal processing (RTP) system. The object placed in the RTP system is at least partly covered by at least one (1) layer comprising silicate glass. Once placed into the RTP system, the object is heated in an atmosphere comprising at least one reactive gas that is reactive to at least one material covered by the glass. Specifically, the object is heated to a temperature sufficient for reflow of the silicate glass within a predetermined time. While the object is being heated, the concentration of the reactive gas is controlled for selective reaction of the gas with the material.
In one embodiment, the atmosphere contained within the RTP system comprises steam in combination with a reactive gas. The reactive gas can be, for instance, hydrogen, oxygen, nitrogen, dinitrogen oxide, ozone, hydrogen peroxide, atomic and/or molecular hydrogen, or in general radicals or mixtures thereof. In general, the volume ratio between the steam and the reactive gas is between about 1:0.01 to about 1:1,000.
According to the process of the present invention, the steam contained with the RTP system is diluted with other gases as described above so that the steam does not oxidize materials covered by the silicate glass.
In an alternative embodiment of the present invention, the atmosphere contained within the RTP system is an inert gas, such as argon or nitrogen. In this embodiment, steam can be present to reflow the silicate glass while the inert gas is used to protect other layers on the substrate. For instance, steam can be present in accordance with the present invention at a concentration insufficient to cause adverse oxidation reactions from occurring.
Other features and aspects of the present invention are discussed in greater detail below.